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Show 1885.] DR. H. GADOW ON THE SPECIES OF RHEA. 317 is remarkable for the still greater length of its toes. The proportional shortness of the toes of the Common Rhea has already been observed by Mr. Cunningham. Mr. Sclater's original statement that the toes are much shorter in his Rh. macrorhyncha than in the Common Rhea cannot be confirmed. The proportions of the femur and tarso-metatarsus to each other permit of no safe conclusions, nor do the dimensions of the pelvis, owing to the considerable alterations undergone by these parts during the individual growth. The scapula of Rh. americana seems to be much longer than that of Rh. darwini, in comparison with the coracoid, although the latter bone in Darwin's Rhea is absolutely stronger. This apparent shortness of the scapula, however, is partly produced by this bone being curved at a sharper angle in Rh. darwini. Muscles. The examination of the muscles of two Rh. americana, two Rh. darwini, and one Rh. macrorhyncha did not yield many interesting variations except for that most variable of all the thigh-muscles, to wit the famous m. ambiens. In the Common Rhea this muscle was typically developed, arising from the pubic spine, and its slender tendon passing the knee to form one of the heads of m. flexor perforatus. In Rh. macrorhyncha the muscle arose from the latero-dorsal aspect of the pubic spine and at the same time from the big crural vein, the muscular and aponeurotic fibres of the muscle having firmly got hold of the ventral aspect of this vein. The right and left side were alike ; the tendon of the muscle passed the knee in the typical way. Rhea darwini, 2 •-The m. ambiens of either side arose from the pubic spine as usual, but its tendon, before reaching the knee, became flattened out and attached itself with a broad fan-shaped and very thin aponeurosis to the patella, in a similar style as the median additional portion of the m. fernoro-tibialis (m. vastus). Rh. darwini, 3» left thigh. The m. ambiens stopped at the knee as in Rh. darwini 2 • Right thigh.-Muscle typically developed and passing the knee with a strong and independent tendon. This abnormal condition of the m. ambiens, which seems to he prevailing in Darwin's Rhea, is the intermediate stage between a typically developed m. ambiens and such forms in which, as in Casuarius, this muscle has lost still more of its independence, and then only forms an additional head of the median part of the portio media m. femori-tibialis s. vasti.-Without an elaborate examination and comparison of the formation of these muscles with their nerve-supply, we should with Garrod come to the conclusion that Casuarius did not possess an ambiens muscle. The assumption of still further reduction of the distal portion of the m. ambiens explains what I have observed in some Passerine birds, e.g. in a specimen of Lanius bentet, in which the m. fernoro-tibialis internus, besides being strongly developed, received in its proximal part a |